What are Altostratus Clouds?

Altostratus clouds form at mid to high-level altitudes (between 2 and 7 km) and are created by a warm, stable air mass which causes water vapor
to condense as it rise through the atmosphere. Usually altostratus clouds are featureless sheets characterized by a uniform color.

In some cases, wind punching through the cloud formation may give it a waved appearance, called altostratus undulatus. Altostratus clouds
are commonly seen with other cloud formations accompanying them.